A. Field of the Invention
The present invention relates generally to overload release apparatus, and more particularly to such an apparatus as applied to a landing gear assembly of an aircraft.
B. Brief Description of the Prior Art
In the aircraft industry, where weight of the aircraft components is such a highly critical factor, it is common to design components to withstand applied loads of a predetermined level plus a certain overload factor. To allow for those exceptional situations where unusually large loading occurs, various types of overload release apparatus are employed to permit certain components to yield in a manner to minimize danger to the occupants of the aircraft and minimize damage to the aircraft. One practice is to use fuse pins or the like which simply give way at a predetermined level of loading. Another is to employ yielding members which will permanently deform under excessive loading to absorb energy and thus cushion the impact.
With regard particularly to aircraft landing gear, to absorb the impact which the landing gear normally encounters in making a landing, generally, there is incorporated in the landing gear energy absorbing devices, such as shock struts. However, under conditions of excessive loading on the landing gear (which could occur, for example, when the aircraft is descending too rapidly or where the landing gear encounters some obstruction on the landing surface), it can be expected that the shock strut or other impact absorbing member would be stressed beyond its design limits so that it and possibly other components of the aircraft would be damaged. Thus, there have been developed in the prior art various devices which employ the above-mentioned practice of using components which will deform permanently under conditions of excessive loading to prevent overstressing of certain components of the aircraft and diminish the impact which is ultimately transmitted to the aircraft. Typical of such devices are the following.
In the Harriman et al patent, U.S. Pat. No. 2,641,423, there is shown a landing gear for a helicopter. The gear comprises elongate tubular members which deform under bending moments to absorb the shock of "hard landings."
The Rayfield et al patent, U.S. Pat. No. 2,961,204, shows a landing device adaptable for space capsules or the like. There are a plurality of telescoping struts, with "cutters" being positioned in engagement with the interior members of the telescoping struts. Upon impact of landing, as the struts move inwardly in telescoping fashion, the cutters cut grooves in the strut member to absorb the impact.
The Westcott, Jr. patent, U.S. Pat. No. 2,997,261, shows a tension rod extending between two pivotally mounted components of a landing gear. Under excessive loading, this tension rod is stretched beyond its elastic limit to absorb the impact.
The Doak patent, U.S. Pat. No. 3,066,888, shows an aircraft having two laterally spaced engines to provide vertical thrust. To prevent damage to the engines in the event of an improper landing, energy absorbing members are mounted in the aft faring of each engine.
The McGehee et al patent, U.S. Pat. No. 3,143,321, shows a shock absorbing strut for a spacecraft and the like. This strut comprises a tubular member mounted to a flared base. Upon impact loading, the tubular member fractures into fragments as it continues to move downwardly over the flared base.
The Fagan et al patent, U.S. Pat. No. 3,716,208, shows a helicopter landing gear where there is a liquid spring mechanism to absorb shocks. This is mounted to a laterally extending plastically deformable member which bends upwardly upon impact to absorb the shock.
Also representative of the prior art is German Pat. No. 1,213,253, issued Mar. 24, 1966.
In addition to the prior art noted above which relates specifically to landing devices for aircraft, the following patents are noted as background information relating to various arrangements of overload release devices.
The Wood patent, U.S. Pat. No. 1,778,477, shows a particular arrangement of a shear pin mounted to a shaft.
The Shaw patent, U.S. Pat. No. 2,391,275, shows a yield link which has a tubular member that collapses under axially loading. One of the suggested uses for such a strut is for the undercarriage of airplanes.
The Westbury patent, U.S. Pat. No. 2,633,037, shows a configuration for a collapsible strut which telescopes under axial loading.
The Walker patent, U.S. Pat. No. 3,185,413, shows a particular device for locating a shear pin used in holding an aircraft prior to launch.
The Mulquin patent, U.S. Pat. No. 3,304,031, also shows a catapult related device for an aircraft, and specifically shows a tension element which fractures under tension loading above a certain level.
The Ratcliff patent, U.S. Pat. No. 3,602,065, shows an arrangement where there is a shear pin on a cranking lever for a cable-type hoist. When the shear pin gives way, it is necessary to replace the pin before the lever again becomes operable, this being a safety feature for this particular type of apparatus.
The Campbell, et al patent, U.S. Pat. No. 3,964,578, shows an automobile related device to absorb shocks in a crash situation. It relates to a particular configuration of a shock-absorbing plate which has slots which permit the plate to deform from a planar configuration upon impact.
The Strizki patent, U.S. Pat. No. 3,967,906, simply shows a mounting for a sign post whereby the upper support member is releasably connected to a lower support by break-away coupling members which are adequate to withstand wind loads and the like, but which will give way upon crash impact, such as would occur when an automobile runs into the sign.
As a matter of general interest, the Sperry patent, U.S. Pat. No. 1,641,700, is noted to show a detachable landing gear in an aircraft. The landing gear is released by pulling a lever which in turn releases a retaining latch.